Generally, synthetic drugs remain "legal" because the chemists making them change the chemical structure enough to get around the specifics of the laws banning certain types of them. "Synthetic marijuana" is really an incorrect name for it. It's a chemical that they spray onto dried organic matter (leaves) so it just looks like mj.
"For several years, synthetic cannabinoid mixtures have been easy to buy in drug paraphernalia shops, novelty stores, gas stations, and over the internet. Because the chemicals used in them have no medical benefit and a high potential for abuse, authorities have made it illegal to sell, buy, or possess some of these chemicals. However, manufacturers try to sidestep these laws by changing the chemical formulas in their mixtures."
You have to ban every chemical formula, then they just make a new one. And the only way to know is to send it to the crime lab which takes forever and costs $ to process.
I've been wondering the same about this craze over "CBD" oil. B/c people are talking about how it's legal and how it helps "cure" everything under the sun. But legally if it is a cannabinoid, cannabidiol, or other cannibus related item, wouldn't that fall under the controlled and dangerous substance act and be "controlled". Beyond that, THC is illegal unless with an RX, and hemp is legal, but has to contain less than some crazy small amount of those agents. So is it a scam, should it be illegal? etc.
I remember when they banned one chemical after another when finding it in "incense" and bath salts. Then they did a blanket, ANY THC or cannabinoid derivative is illegal, and it shut down "MOJO and NOLA DIAMOND" almost immediately.
I remember when the incense/mojo/spice crap started, it was mostly 40 year old children that we caught doing stupid stuff with it. These idiots smoking "some random chemical" sprayed on some potpourri deserve whatever legal and/or health problems they wind up in.